In recent years elliptic waveguides, especially corrugated elliptic waveguides have gained importance and application because of their flexibility. In order to connect such elliptic waveguides in a reflection-free manner with conventionally used rectangular waveguides, transformation devices are required which are generally employed for connecting waveguides of varying cross section in a reflection-free manner or at least only at low reflection.
It is known to make transformation devices by galvanoplastic methods or through precision casting. These manufacturing methods, have the drawback, that the very narrow tolerances required to achieve a low reflection coefficient over a broad band width cannot be attained so that cumbersome and complicated aftertreatments are required and in addition adjusting pins must be provided and individually calibrated.
From the German patent DE-PS No. 19 48 156, there is known a transformation device for connecting a rectangular waveguide with an elliptic waveguide which can be produced through cutting treatment. This method is less expensive and more precise than the previously mentioned manufacturing methods. Such a transformation device has the cross section of the rectangular waveguide to be connected whereby the broader sides of the rectangular cross section have a stepped recess over a length of lambda/4 which is rotationally symmetrical to the axis of the transformation device.
The German patent DE-PS No. 20 17 042 describes a transformation device which includes a waveguide element defined by several transforming sections successively arranged in axial direction and with a length of lambda/4 for increasing the band width. The diameter of the rotationally symmetric recesses in the broader sides decreases step-by-step in direction from the connection plane with the elliptic waveguide to the connection plane with the rectangular waveguide.
Such a transformation device has the drawback that the individual stepped recesses have to be bored at an extreme precision and, further, it is difficult to provide within the individual transforming sections recesses or continuous transitions from section to section (as it is known per se from the Swiss patent CH-PS 551 086). A further drawback is the fact that transformation devices with a plurality of stepped recesses are of considerable axial length.